1. Field of the Invention
The present invention relates to a sequential polygon approximation apparatus for a contour and a method thereof, and particularly to an improved sequential polygon approximation apparatus for a contour and a method thereof which are capable of sequentially extracting a vertex in the order of a contour pixel when performing a polygon approximation so as to code a shape information.
2. Description of the Conventional Art
As an international coding standard, there are MPEG-1, MPEG-2, H.261, etc. These coding standards are directed to using a block based coding technique such as a discrete cosine transform (DCT). The motion compensation is processed by the block unit of each image frame with respect to a moving object.
Since the above-described block based coding technique is directed to performing a coding with respect to the entire frames, the amount of the generated information is increased, and it is impossible to transmit a motion picture signal through a channel such as a public telephone network or a wireless communication network which are very slow to communicate to each other, for thus degrading the picture quality.
In order to overcome the above-described problems, an object-oriented coding technique which is not a block based technique has been studied in the industry. An effective coding method of a shape information (a contour) of an object is needed.
The conventional techniques for decreasing the amount of the shape information with respect to the moving object according to the vertex-based coding are as follows.
There are an article "Predictive contour coding for an object-oriented analysis synthesis coder", IEEE International Symposium Information Theory, San Diego, Calif., U.S.A, January 1990, at page 75, made by M. Hotter, and an article "Object-oriented analysis synthesis at low bit rates", IEEE Transaction on Circuits and system for Video Technology, Special Issue on very low-bit rate video coding, vol 4, No. 3, June 1994, at pages 228 through 235.
In accordance with the above-described techniques, the entire contours of the moving object region are approximated, and the motion compensation of the vertexes used for the approximation is predicted, and the error thereof is transmitted.
However, in accordance with the conventional method which is directed to considering the entire shape information, the amount of the entire data which is transmitted is great, for thus degrading the picture quality.
In addition, the polygon approximation method which is directed to approximately expressing the contour of the moving object is used for an object recognition, an image analysis, an image coding, etc, and the applicable range thereof becomes wider.
In particular, since the image coding considering the object or content becomes a major technique for MPEG-4 based on the concept of a video object plane (VOP), the polygon approximation method becomes one of important methods of the shape information together with the shape information transmission of an object.
FIGS. 1A through 1D are views illustrating a conventional polygon approximation process.
First, when there is given an open contour, namely, both ends of the contour are not connected, as shown in FIG. 1A both ends thereof are connected to each other.
In addition, as shown in FIG. 1B, the points in which the distance to a pixel forming a contour in the vertical direction with respect to a straight line is the maximum are computed as a new vertex, and a new vertex is connected to the respective two end points by a straight line.
As shown in FIG. 1C, the straight lines are repeatedly connected until the maximum distance to the contour pixel in the vertical direction with respect to the straight line becomes smaller than the threshold value (hereinafter, referred to `thr-dmax`, and finally a polygonal straight line is obtained as shown in FIG. 1D.
In addition, if the contour is closed, two pixels in which the straight line among the pixels are the maximum are connected. In addition, in the case of the open contour, the above-described processes are repeated, for thus obtaining a polygonal straight line.
Here, the threshold value is given as the maximum error between the contour and the polygonal straight line which are permitted during the polygonal approximation for the contour.
However, in the conventional polygonal approximation, the maximum error in each polygonal straight line range is generated when the maximum error is smaller than the threshold value. In addition, the number of vertexes are disadvantageously increased due to the above-described intervals.
In addition, since the above-described problems increase the amount of the data to be transmitted in the image coding method which is directed to transmitting the position information of the vertex, for thus lowering the coding gain.